1. Technical Field
The present invention relates to a screwdriver having a screw gripping feature. The present invention relates more particularly to a screwdriver for gripping a Phillips-head screw. Other embodiments of the present invention relate to a screwdriver for gripping a plain slotted screw or hex head screw.
2. The Prior Art
In U.S. Pat. No. 2,445,383 to Barlow, a screwdriver is shown having a two-part expanding bit. The bit is for use with a standard slotted screw having a single slot therein. As seen in FIG. 12 of Barlow, the two-part expanding bit has a pair of inclined contacting surfaces which face one another, so that a force applied urging the two-part expanding bit portions together causes the two parts to be displaced sidewardly and against the walls of the slot formed in the screw. The inclined contacting face of the two parts of the bit can be considered as a first "camming" surface, which uses the inclined contact surfaces (22, 22 of Barlow) to create a translation of force from an axial direction along an axial line passing through the center of the slot of the screw, into a transverse force to that axial line, namely against the side walls of the slot in the screw. Depending on the angle of inclination of the contacting surfaces 22, 22 of Barlow, a mechanical advantage can be gained which would in effect multiply the force applied axially so that an even greater force would be applied transversely to the side walls of the slot formed in the screw.
Additionally, in the above-noted Barlow reference, a second "camming" means is used, namely the sleeve 23 acting against the parts 17 and 19 urging them toward one another. The parts 17 and 19 are two blade halves which are resiliently biased to a first position when the sleeve is against the handle, as seen in FIG. 1 of Barlow. As seen in FIG. 2 of Barlow, however, the sleeve 23, in moving away from the handle portion 25, exerts a force on the bit parts 17 and 19, which due to the relatively low angle of incline of the bit parts 17 and 19 results in a relatively large multiplication of the force applied. That is, the manual force exerted on the cylinder 23 during manual operation thereof is multiplied based upon the leverage principle of mechanical advantage so that a far greater force is achieved urging the two bits 21, 21 toward one another. As noted above, the force can be further multiplied due to the angle at which the contacting surfaces 22, 22 are relatively disposed. The Barlow reference does not suggest use of a two-part expanding bit for use with a Phillips-head screw, and also the Barlow reference requires the use of two different "cammingp" means.
In U.S. Pat. No. 3,224,479 to Osborn et al, an expanding bit screwdriver is shown having a movable sleeve and a two-part bit. A pair of bit interceptors 13 are shown in FIGS. 4 and 5 of Osborn et al., which are engaged by the sleeve during axial movement thereof, to force sliding movement of the expandable parts 12a and 12b relative to one another along a sliding contact surface referred to as a slip plane 12c. The interceptors 13 are a camming surface acted upon by the sleeve, and the slip plane 12c is a second camming surface which causes lateral relative movement of the expandable parts 12a and 12b in a direction which is perpendicular to the slot of a slot head screw, thereby giving rise to frictional contact forces to retain the screw to the expanding bit.
U.S. Pat. No. 2,625,971 to Bier shows a screw-holding attaching device for cruciform bit screwdrivers. Here, the screwdriver is made to retain a Phillips screw thereon by use of a camming or wedging action by spreading of tips 26 until outer faces of the tips are forced tightly against the sidewalls of the kerf of the screw and coact therewith.
In U.S. Pat. No. 3,208,489 to Walker, et al., a Phillips-head screw starter is shown having a relatively complex bit shape in the form of a pair of opposed V-shaped portions 26,26 as shown in FIG. 5 thereof. The portions are resiliently biased apart, and a sleeve initially maintains them in their abutting configuration, such that retraction of the sleeve permits expansion thereof so as to frictionally retain a Phillips head screw. Here, camming is used only to initially form the generally X-shaped head by positioning the two V-shaped portions, and removal of the camming action permits spreading of the V-shaped portions.
In U.S. Pat. No. 3,288,184 to Kyser, another Phillips head screw starter is shown having a pair of V-shaped bits which move apart from one another by retraction of a camming member. The V-shaped portions are resiliently biased apart, such that the camming member holds them together for insertion into a Phillips head screw. Here, the spreading of the V-shaped portions occurs in a direction which generally bisects each V-shaped portion.
In U.S. Pat. No. 3,354,919 to Sugaya, another type of screwdriver is shown, having an embodiment usable in a hex head screw socket. A locking device is used in these embodiments, which rotates internally of the screwdriver shaft to cause gripping of the screw by the screwdriver blade.
In U.S. Pat. No. 3,003,528 to Landeau, a screw holding screwdriver is shown having a pivot 19 and a sleeve 24 which cooperates with a camming surface, such that the screwdriver blade tip pivots about the pivot point to cause relative displacement of two halves of a screwdriver blade tip, to frictionally lock or grip a slot head screw.
It is a problem in the prior art to provide a screwdriver blade tip which is capable of frictionally retaining a screw thereon, particularly for Phillips head screws. It is also a problem in the prior art to provide a relatively simple mechanism for frictionally retaining screws on the tip of a screwdriver using a single camming surface to cause relative movement of two portions of a screwdriver bit.